1. Field of The Invention
This invention relates to a scanning-line interpolation apparatus for converting signals representing an image obtained by an interlaced scanning to signals representing another image obtained by a non-interlaced scanning.
2. Description of The Related Art
A conventional apparatus for detecting a motion vector of an image and moving an image of the preceding field according to the detected motion vector to perform an interpolation of scanning lines is disclosed in, for example, Japanese Unexamined Patent Publication (Tokkyo Kokai Koho) Official Gazette No. 1-108886.
FIG. 1 is a schematic block diagram for illustrating the configuration of the conventional scanning-line interpolation apparatus. Reference numeral 31 denotes an input terminal, from which a signal representing image information obtained by what is called a 2:1 interlace scanning (namely, an odd-line interlacing) is input; 32 to 34 field memories; 35 a motion detecting circuit; 36 a mixer circuit; 37 and 38 time-base compression circuits; 39 a switching circuit; 40 an output terminal, from which a signal representing image information obtained as a result of a non-interlaced scanning; 41 a motion-vector detecting circuit; and 42 a position moving circuit.
When a signal representing image information obtained by a 2:1 interlace scanning is supplied to the input terminal 31, a signal representing image information of a current field is output from the field memory 33. Simultaneously, a signal representing image information of the succeeding field and a signal representing image information of the preceding field are output from the field memory 32 and the field memory 34, respectively. Then, the signal representing image information of the succeeding field and the signal representing image information of the preceding field are input to the motion vector detecting circuit 41 whereupon a motion vector corresponding to an inter-frame motion is detected. Subsequently, a signal representing the detected motion vector is input to the position moving circuit 42 whereupon an image represented by the image information of the preceding field is moved by a distance, which is one-half the magnitude of the motion vector, in the direction of the motion vector.
Meanwhile, the signal representing image information of the succeeding field and the signal representing image information of the preceding field are also input to the motion detecting circuit 35 whereupon a motion is detected with regard to each pixel from an absolute value of the difference in luminance between the preceding and succeeding fields.
An output signal of the position moving circuit 42 and the signal representing the image information of the preceding field are input to the mixer circuit 36. Thereafter, a signal obtained by mixing these signals is output therefrom. At that time, the mixer circuit 36 changes a mixing ratio according to the output of the motion detecting circuit 35.
Moreover, the signal representing the image information of the current field is input to the mixer circuit 36. In case where a motion vector cannot be detected by the motion vector detecting circuit 41, a signal representing a result of an interpolation of the scanning lines of the current field only according to the image information of tile current field is output from the mixer circuit 36.
The signal representing the image information of the current field and the signal output from the mixer circuit 36 are input to the time-base compression circuits 37 and 38, respectively, whereupon the image represented by the signal is compressed or reduced to a scale of half of the original size thereof with respect to time. Thereafter, the switching circuit 39 switches one of the outputs of the time-base compression circuits 37 and 38 to the other of the outputs thereof every horizontal scanning interval. Then, the selected output of the time-base compression circuits is output from the switching circuit 39. Thus a signal representing image information to be obtained by a non-interlaced scanning is output from the output terminal 40.
However, in case of the above described apparatus, an interpolation of the scanning lines of the current field is performed by mixing the signal representing the image information of the preceding field with the signal obtained by shifting the image by a distance, which is one-half the magnitude of the detected motion vector, in the direction of the motion vector. Therefore, if the detected motion vector is incorrect, an interpolation of the scanning lines is effected according to incorrect image information with the result that picture quality is degraded. Accordingly, it is necessary for preventing the degradation in picture quality to judge whether or not a motion vector is correctly detected and to obtain a signal representing the result of the interpolation of the scanning lines according to the judgement.
In case of an ordinary image, there is a high correlation between neighboring pixels. Hence, there is a high correlation between a motion vector detected in a block and another motion vector detected in a neighbouring block. Namely, in case where correct motion vectors are detected, there is a high correlation between motion vectors of neighbouring blocks. In contrast, in case where incorrect motion vectors are detected, there is a low correlation between motion vectors of neighbouring blocks. Therefore, it can be judged from a comparison of a motion vector detected in a block with another motion vector detected in a neighbouring block whether or not the motion vector is correctly detected in the block.
It is, accordingly, an object of the present invention to provide a scanning-line interpolation apparatus which can prevent an interpolation of scanning lines from being performed according to an incorrect motion vector by judging whether or not a detected motion vector is correct and also prevent the degradation in picture quality.
Meanwhile, it is confirmed that human visual perception extracts structural features such as edge portions included in an image. Therefore, if a motion vector detected in a block containing an edge portion is incorrect, there occurs deterioration in picture quality of an edge portion, which is especially apt to come under a viewer's notice. Consequently, this leads to degradation in visual picture quality of an entire image.
It is, accordingly, another object of the present invention to provide a scanning-line interpolation apparatus which converts a signal representing an image, which is obtained by a 2:1 interlaced scanning, to a signal representing an image, which should be obtained by a non-interlaced scanning, by judging whether or not a detected motion vector is correct, and changing judging conditions with regard to an edge portion, which is especially apt to come under a viewer's notice, to thereby prevent deterioration in picture quality of the image.